In alkaline water electrolysis, electrolysis of pure water, electrolysis of non-purified water, brine electrolysis, electrolysis of a chloride aqueous solution, a bromide aqueous solution, a hydrochloric acid aqueous solution, or a sulfuric acid aqueous solution, or the like, hydrogen gas is generated by electrolysis.
An example of an electrolytic apparatus and an electrolytic method in which hydrogen gas is generated is an alkaline water electrolytic apparatus and an alkaline water electrolytic method described in Patent Literature 1. In the electrolytic apparatus and electrolytic method of Patent Literature 1, an anode liquid and a cathode liquid made of a gas-liquid mixed fluid and generated in an anode chamber and a cathode chamber are collected in a common circulation tank to be mixed in the circulation tank. Thereafter, the mixed liquid is circulated and supplied into both electrolytic chambers of the anode chamber and the cathode chamber. The electrolysis is continuously performed while the concentrations of the electrolytic solutions supplied into both the electrolytic chambers are made the same and are maintained at a constant concentration all the time by mixing the anode liquid and the cathode liquid in the circulation tank.